A variety of fields, including the fields of cosmetic materials, household items, and release agents, require the formation of a high-viscosity organopolysiloxane as a fine emulsion. However, when a high-viscosity organopolysiloxane is subjected to direct emulsification, the limit for the particle size of the emulsion particles is about several microns, and obtaining a finer emulsion is difficult. As a result, a variety of investigations have been undertaken into methods of producing emulsions by emulsion polymerization, with the aim of obtaining fine emulsion particles.
For example, methods in which a cyclic siloxane oligomer is subjected to emulsion polymerization in an emulsified state using a strong acid or a strong base are already known (Patent Documents 1 and 2). By using these methods, emulsions can be obtained in which the particle size of the emulsion particles is 300 nm or less.
However, in recent years, concerns have been raised about the effects of octamethylcyclotetrasiloxane as an environmental impact substance, and products in which the octamethylcyclotetrasiloxane content has been suppressed are now being demanded. In the methods disclosed in Patent Documents 1 and 2, it is known that the organopolysiloxane contained within the obtained emulsion contains 40,000 ppm or more of octamethylcyclotetrasiloxane, and therefore methods of suppressing the amount of octamethylcyclotetrasiloxane produced are now being investigated.
For example, in one known method for producing an organopolysiloxane emulsion, an emulsion composed of (a) an organopolysiloxane represented by a general formula: HO(R2SiO)mH (wherein R represents identical or different monovalent hydrocarbon groups, and m represents a value corresponding with a viscosity at 25° C. within a range from 30 to less than 10,000 mm2/s) and containing an amount of condensation-unreactive organosiloxane oligomers having 20 or fewer silicon atoms of not more than 5,000 ppm, (b) a polymerization catalyst (although in those cases where a surfactant having a catalytic action is used as the component (c), the component (b) is unnecessary), (c) a surfactant, and (d) water [in an amount of 30 to 1,000 parts by mass per 100 parts by mass of the component (a)] is subjected to an emulsion polymerization under conditions including a temperature of not more than 40° C. and a polymerization time of not more than 40 hours, and the amount of condensation-unreactive organosiloxane oligomers having 20 or fewer silicon atoms within the produced organopolysiloxane exceeds 1,000 ppm but is not more than 10,000 ppm (Patent Document 3). However, with this method, a problem arises in that even if the emulsion polymerization is conducted for 24 hours using an emulsification device such as a high-pressure Gaulin homogenizer, the viscosity of the organopolysiloxane in the emulsion is limited to 1,000,000 mm2/s, and if the condensation time is lengthened in order to obtain a higher viscosity siloxane, then the amount of octamethylcyclotetrasiloxane exceeds 3,000 ppm.
As a result, being able to adjust the viscosity of the organopolysiloxane in the emulsion to a desired value using as short an emulsion polymerization time as possible is highly desirable, not only in terms of enhancing the production efficiency, but also from the viewpoint of suppressing the amount of octamethylcyclotetrasiloxane contained within the organopolysiloxane in the emulsion.